yarnpkg/yarn

Multiple sub-scripts do not output progressively

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#4423 opened on Sep 12, 2017

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Description

I have package.json scripts like this:

"scripts": {
    "lint:all": "yarn run lint:project-a && yarn run lint:project-b && yarn run lint:project-c",
    "lint:project-a": "cd project-a && yarn run lint",
    "lint:project-b": "cd project-b && yarn run lint",
    "lint:project-c": "cd project-c && yarn run lint"
}

This is the output from npm@5.4 which is what I would say is "expected":

$ npm run lint:all

> example@1.0.0 lint:all c:\dev\example
> yarn run lint:project-a && yarn run lint:project-b && yarn run lint:project-c

yarn run v1.0.1
$ cd project-a && yarn run lint
Done in 8.34s.
yarn run v1.0.1
$ cd project-b && yarn run lint
Done in 8.26s.
yarn run v1.0.1
$ cd project-c && yarn run lint
Done in 10.57s.

Yarn produces this:

$ yarn run lint:all
yarn run v1.0.1
$ yarn run lint:project-a && yarn run lint:project-b && yarn run lint:project-c
Done in 48.05s.

and the wait is quite long. Is this expected behavior or possibly a bug?

Node 8.4.0, Yarn 1.0.1, Windows 10

Contributor guide

Tech stack
javascriptnodejs
Domain
cli
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
basic understanding of yarnfamiliarity with child process streams
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
The issue reports that when running multiple sub scripts sequentially with `&&`, Yarn buffers all output and displays it only after all scripts finish, unlike npm which shows output progressively. Investigate how Yarn spawns child processes and handles their stdout/stderr streams. Look in the `src/util/execute lifecycle script.js` or similar files for how output is collected and flushed. Check if there's a way to inherit the parent process's stdio to achieve progressive output. Note that the repository (1.x line) is frozen, so any fix would likely need to target the 2.x line at https://github.com/yarnpkg/berry.